Dipteran endoparasitoid infestation actively suppressed host defense components in hemocytes of silkworm Bombyx mori for successful parasitism

Abstract

Infestation of commercially important silkworm Bombyx mori by dipteran endoparasitoid Exorista bombycis causes ~20% revenue loss. Though invasion has induced hemocyte encapsulation and melanisation of invaded larva, strategies to compromise with host-defense system by dipteran endoparasitoids is unknown. In the present study variation in genome wide gene expression was analyzed by utilizing microarray data acquired from hemocytes collected at 6 h after invasion that showed significant (P < 0.05) up-regulation of 423 genes and down-regulation of 587 genes. Among them 11 detoxification genes and 34 immune genes down-regulated showing repressed defense reactions substantiated by reduced activity of detoxification enzymes esterase and FMO in early stage of infestation. The down-regulated genes were enriched after comparing with control and by filtering unreliable probes. GO annotation of significantly (P < 0.05) down-regulated genes was used for clustering and categorization of functionally related defense processes. Networking of interacting partners of down-regulated defense genes showed relatedness among the down- regulated biological processes viz., Wnt signalling, DNA repair, transcription, catabolism, glutamine metabolism, components of cytoskeletal structure and transport. These clusters perform immune responses, signalling, stress responses, cell redox homeostasis, cytoskeletal organization, glutamine, glycogen and chitin metabolism, protein, lipid and carbohydrate metabolism and transmembrane transport. Autophagy, apoptosis, cell adhesion, cell growth and cellular lipid metabolism also showed down-regulation independently. Down-regulation of defense genes, interacting components and low detoxification enzyme activity in early infestation revealed active suppression of host defense at genic, enzymic and interactome level which is an unknown anti-defense mechanism of dipteran endoparasitoids.